AMD clarifies reports of Zen 2's 29% IPC boost over Zen

What is IPC?

AMD clarifies reports of Zen 2's 29% IPC boost over Zen

Over the past few days, news outlets from across the techno-web have been discussing the performance implications of AMD's DKERN +RSA benchmarking data, a data point that lies hidden within the footnotes of AMD's Zen 2 Next Generation EPYC press release.

In a recent statement to some tech outlets, AMD has clarified that the benchmark's report of a 29.4% IPC uplift is based on a specific workload and that this value should not be used to set expectations for general performance improvements per clock with Zen 2. As always, a single data point cannot be used to define an entire product.

For starters, let's state what IPC means. IPC stands for Instructions Per Clock, the number of instructions that can be processed by a CPU in any given clock cycle. A processor with a higher IPC than another will offer greater performance levels than a CPU with lower IPC at the same clocks, though it is always worth noting that IPC in itself is workload dependent.

As we said in our previous article about Zen 2's 29.4% IPC boost, the workload that AMD used is based on both integer and floating point workloads, utilising Zen 2's reported doubling of floating point performance to great effect during their testing. It stands to reason that a workload that is based almost entirely on floating point performance will see greater performance boosts, or IPC lifts, in that scenario, and wholly integer tasks will see smaller performance increases.

While PC consumers like to use IPC as a catch-all term for performance per clock, the reality is that workload matters and IPC gains in one area will not automatically translate to gains in another. Anyone expecting Zen 2 to offer a 29.4% performance boost in all workloads over Zen at the same clocks is expecting too much, and needs to temper their expectations. Below is a statement from AMD on the matter, which comes via Bit-tech.

The data in the footnote represented the performance improvement in a microbenchmark for a specific financial services workload which benefits from both integer and floating point performance improvements and is not intended to quantify the IPC increase a user should expect to see across a wide range of applications,

We will provide additional details on "Zen 2" IPC improvements, and more importantly how the combination of our next-generation architecture and advanced 7nm process technology deliver more performance per socket, when the products launch.

On the core side, Zen 2 offers a redesigned execution pipeline, featuring an improved branch predictor, a re-optimised instruction cache, better instruction pre-fetch and a larger Ops Cache, all of which will help increase Zen 2's IPC (performance per clock) in a variety of workloads. Early leaks have suggested that AMD's Zen 2 architecture will offer a 13+% boost in performance over Zen 2 in standard non-AVX applications, though AMD has not confirmed this data.

Like every architectural leap in processor design, performance boosting techniques are largely application dependent, with each design change delivering performance advances to specific aspects of a processor's functionality, rather than offer a ?% gain in every application under the sun.

When combined with possible clock speed boosts, AMD's Zen 2 processors could offer a significant leap over their Zen/Zen+ counterparts over a range of PC applications, though we will have to wait a while before we start seeing real-world performance numbers from AMD's next-generation CPU designs.

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